If It's Removable, Put It Between Commas

A bank official replied to a prospective client, and with the reply enclosed an annual report.  Unfortunately, the official wrote this sentence:

I am enclosing an annual report that shows we are debt-free.

The dependent clause "that shows we are debt-free" is not separated by a comma.  That lack of separation implies that the clause is essential to describe which annual report is being sent. Are there others? Those reports may tell a different financial story!

Conclusion: if the descriptive word(s) are removable (redundant), then use a comma or a pair of commas to set them apart from the sentence.  To imply the bank's integrity, the bank official could have written this sentence:

I am enclosing an annual report, which shows we are debt-free.

Personally, I would have gone on to make the sentence even more precise:

I am enclosing our latest annual report, which shows that we are debt-free.